Submerged combustion distillation



United States Patent SUBMERGEB CGWUSTIQN BESTELATi-GN Arthur L. Saxton,Warren Township, Somerset County, Harold N. Weinberg, East Brunswick,and Edward E. Higgins, Chatham, NHL, assignors to Esso Research andEngineering ompany, a corporation of Delaware Filed Dec. 12, 196%, Ser.No. 75,283 8 Qiaims. (3. 2-034l) The invention relates to an improveddistillation methad for fractionating petroleum oils. More specificallythe invention relates to a novel method for producing asphalts fromasphalt-containing crudes.

Distillation is one of the chief methods for fractionating petroleumoils. The basic distillation concept is to charge the petroleum oil,crude, etc. into a distillation column and supply heat to the system byeither heating the feed, the bottoms or the bottoms recycle by means ofindirect heat exchangers or furnaces. The cost of heating the system ishigh and represents a major portion of the operating expenses of anydistillation unit. it is, therefore, desirable to provide heat to adistillation zone with the least amount of expense and at the highestefdciency possible. The instant invention ers such a process whereinhigh heating eihciency is obtained.

Additionally the instant invention affords a method whe ein cut pointswhich nomally would require subatrnospheric operating conditions may beeffected at atmospheric pressure. Also the instant invention by virtueof the above permits investment and operating economics overconventional heating methods.

It is Well known that asphalt is a major sour e of material for roadconstruction for it provides adequate roads at economical prices. Asidefrom its use as a roadbuilding material, asphalt finds use in houseconstruction for waterproofing, tile cements, shingles, linoleumbacking, and caulking compounds. Furthermore, it constitutes the basicbinder for such diverse products as coal briquettes, paints, expansionjoint fillers and as an adhesive to name only a few of its myriad ofapplications. The advantage of providing low cost methods to produceasphalt are thus readily apparent from the market avaflable to thismaterial.

In the past, two methods have predominated in the manufacture ofasphalt. One is steam distillation at atmospheric pressure in a batch orcontinuous operation. This method is somewhat limited inuse, for it isrelatively slow and frequently leads to incipient cracking, especiallywith high boiling asphalt crudes. The second method is a vacuumdistillation process comprising two ipe still distillation units. In thefirst pipe still, which is operated under atmospheric pressure, theasphaltic crude is distilled to separate therefrom the lighterconstituents such as naphtha, kerosene, heating oil and gas oil, Theresidual material is sent to the second pipe still unit wherein it isdistilled under a vacuum to separate the heavy gas oil from theasphaltic constituents. Both units require substantial heat inputs. Thisprocess is adequate for the production of asphalts but because thesecond stage must be operated under a vacuum, equipment cost issubstantially increased and the operating costs are extremely high.

It is an object of the instant invention to provide an improved methodfor fractionating petroleum feeds by distillation.

It is also an object of the instant invention to provide a methodwhereby cutpoints may be obtained by distillation at atmosphericpressure which heretofore required operating under a vacuum.

t is a further object of this invention to provide a method for moreefficiently supplying heat to a distillation step.

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Furthermore, it is an object of the invention to provide a method forproducing asphalt in a more economical manner.

Briefly, the invention in its broadest form relates to supplying heat toa distillation zone by submerged combustion. Basically, submergedcombustion is combusting a mixture of fuel and air and releasing tieflue gas therefrom directly into the liquid to be heated, at bottomsfraction in the distillation zone or a bottoms recycle stream. The hightemperature flue gas is discharged below the surface of the liquid andpasses upwardly through the liquid and the distillation zone. The directcontact between the hot fiue gas and the liquid and the violentagitation caused thereby effects unusually high heat transfer rates andthermal efhciency is or better.

in regard to the recovery of high cut-point material, such as asphalt,there has been developed an integrated system whereby the feed ispreheated with overhead fractions from within the system to form agaseous, lowboiling fraction and a residuum which is subsequently heateddirectly by submerged combustion. In this process the crude, afterpreheating in the manner discussed in more detail hereinafter, isintroduced into a flashing zone to remove the light constituents, suchas naphtha and other low boiling materials. The reduced crude is thendirected to a submerged combustion zone where a mixture of fuel and airis burned and the combustion products released below the surface of theliquid in the combustion zone. vapor overhead comprising combustionproducts and vaporized components of the reduced crude is then employedto preheat the crude thereby resulting in the condensation of thevaporized components of the reduced crude and allowing separationthereof from the combusti n products. The overhead from the flash zonemay likewise be used to preheat the crude.

It is apparent that this method has economical advantages, for itprovides a more efficient heating system, high cut points without theuse of a vacuum, and eliminates the more costly equipment necessary forvacuum separation.

Other objects and advantages of the instant invention will be apparentfrom the more detailed description of the invention which follows.

FIGURE 1 is a schematic diagram of the preferred embodiment of theinstant invention.

FIGURE 2 is a schematic diagram of another embodiment of the instantinvention.

Referring to FEGURE 1 there is illustrated an improved process forproducing asphalt from an asphaltcontaining crude and the preferredmethod of the instant invention. Feed, such as a Tia Juana medium crude,is obtained from a suitable source and directed through line 1 intopreheater 2, a heat-exchanger of conventional design. Stream 3, whichwill be discussed hereinafter in more detail, is used as the heatingmedium in preheater 2. The crude passes from preheater 2 through line 4into a second preheater 5, which is a heat-exchanger of any conventionaldesign. Stream 6, which will be discussed hereinafter in more detail, isemployed as the heating medium in preheater 5.

tream 7 directs the crude, which has now been heated to a temperature inthe range of about 450 to 650 F., to a flash zone 8 wherein the naphtha,light ends and middle distillates are flashed off overhead and removedfrom the fiash zone by line 3. The cut-point of the materials flashedoff in zone 3 will be a function of the temperature of stream 7 enteringthis zone. As it is preferred that all the middle distillates be flashedand recovered in line 3, it is preferred that stream 7 be heated to atemperature in the range of 600 to 650 F., thus providing a cut-pointsuficiently high to flash off most of the middle distillates. Flash zone8 is normally operated at approximately atmospheric pressure, thoughpressures in the range of 5 to 25 p.s.i.g. may be employed.

Flash zone 8 may be merely a tank wherein stream 7 is discharged forflashing. On the other hand it may be an atmospheric pipe still whereintrays and pumparounds are provided to effect additional separation ofthe flashed material. The former apparatus is obviously the cheaper oneand is preferred if it is unnecessary to effect such additionalfractionation of the flashed material.

The overhead stream 3 from the flash zone is directed to preheater 2wherein it is condensed by resultant heat transfer to the crude inline 1. The condensed overhead is recovered inline 13 for use asdesired.

The residue from flash zone 8 is passed via line 9 to submergedcombustion zone 10, which may be of a similar construction to Zone 8with the addition of combustion zone 16. Zone 10 is operated atpressures within the range of about 0 to p.s.i.g. The operatingtemperature in zone 10 will be in the range of about 650 to 950 F.,preferably 700 to 800 F. depending on the cut-point desired. Generallyit is desired to merely remove the gas oil fraction of the crude in theoverhead from zone 10.

The liquid level of the bottoms in zone 10 is indicated at 14. Belowthis level there is located a combustion zone 16 wherein fuel from line11 is ignited in the presence of an oxygen-containing gas, such as air,from line 12. The combustion products, i.e., flue gas, from thecombustion Zone 16 pass into and upwardly through the liquid bottomscausing direct heat exchange therewith and violent agitation of theliquid. Combustion zone 16 may be any apparatus suitable to effect thiscombustion and release of combustion products below the level of aliquid. Many such types of apparatus are well known and any would besuitable to effect the improvements of the instant invention. Fuelssuitable for employment in zone 16 would be heavy or light hydrocarbonfuel oil or any single gaseous hydrocarbon or mixture of gaseoushydrocarbons. The particular fuel employed, however, is not critical tothe instant process.

The use of the submerged combustion step has the effect of flashing thehydrocarbon stream under a partial vacuum and cut points may be obtainedwhich heretofore would require subatmospheric distillation and equipmentsuitable therefor. This may readily be seen by a more detailedexamination of the circumstances. It is well known that the totalpressure of a mixture of gases is the sum of the individual partialpressures. Thus the pressure in zone 10 is the sum of the partialpressures exerted by the flue gas and the hydrocarbon vapors caused byheating. Therefore, if zone 10 is at atmospheric pressure, the partialpressure of the hydrocarbon vapors will be equal to the total systempressure multiplied by their mole fraction in the vapors. Grdinarily,the hydrocarbon partial pressure will be in the range of l to 10p.s.i.a. It is thus apparent that submerged combustion will have theeffect of permitting separations which would otherwise have to beconducted in a vacuum flash or distillation Zone which would requireequipment capable of withstanding subatmospheric operating conditions.Such equipment is far more expensive to construct and operate thanequipment suitable for atmospheric operating conditions.

The overhead 6, which is a mixture of flue gas and vaporizedhydrocarbons from the reduced crude, is directed to preheater 5. Stream6 will generally be at a temperature in the range of about 700 to 800 F.and preferably contain those hydrocarbons boiling between 600 F. and1100 F. However, it may contain hydrocarbons boiling in any rangebetween 350 and 1200 F. In preheater 5 heat exchange occurs which causesthe condensation of the hydrocarbons which were vaporized from thereduced crude and were taken off in stream 6, thereby allowing an easyseparation of these hydrocarbons from the flue gas in separator 18. Theflue gas is withdrawn in gaseous form by line 19 while the condensedhydrocarbons are withdrawn through line 20. If desired a portion ofthese condensed hydrocarbons may be recycled to zone 10.

The bottoms from zone 10 is withdrawn via line 17 and is the recoveredasphalt which may be used as desired. The heat which it contains may beutilized by contacting it in heat-exchange relationship with the crudeemployed as feed in the process.

It has been found that the volume of the flue gas vapors released by theburner 16 is not always suflicient to reduce the partial pressure of thehydrocarbons so as to permit stripping the reduced crude to asphalt. Toeffect this the burner must be over-fired which results in a generalover-heating of the system which is undesirable because of thepossibility of cracking, coking, and the need for more expensivematerials of construction. It has been discovered that this additionalheat required may be removed by injecting water via line 18 into zone 10below the liquid level. The water absorbs the additional heat and isvaporized to steam which has the ancillary effect of producing morestripping vapors. Therefore, water injection produces additionallyrequired stripping vapors with a minimum expenditure for fuel. Any knownliquid injection apparatus would be adequate to effect the advantages ofthis process modification. For the above reasons the use of stream 18 isa preferred embodiment of the instant invention when extremely high cutpoints are required.

FIGURE 2 represents another embodiment of the instant invention. Theprocess is basically the same as that shown in FIGURE 1 with theexception that submerged combustion zone 10 is replaced by atmosphericpipe still 30 and reboiler zone 40. Stream 9 from flash zone 8, as shownin FIGURE 1, is directed to atmospheric pipe still 30. Still 30 isoperated at a temperature in the range of about 650 to 800 F., so theoverhead therefrom will have a cut point in the range of about 600 to900 F. depending on the partial pressure of flue gas entering via line35 and on whether or not extraneous stripping gas, such as steam, inintroduced through conduit 44. Other fractions, such as a heavy gas oilfraction, etc., may be withdrawn, if desired, as side streams. Thebottoms stream 31, which will be at a temperature in the range of about650 to 800 F., is directed to reboiler zone 40 which contains asubmerged combustion unit 32 which may be similar in all respects toburner 16 discussed hereinbefore in relation to FIGURE 1. Fuel and anoxygen containing gas may be supplied thereto in the manner discussedhereinbefore by lines 33 and 34. Zone 40 employs operating conditionsessentially the same as that of zone 10 discussed hercinbefore.

The bottoms from reboiler zone 40, which will be at a temperature in therange of about 700 to 900 F., is withdrawn via line 37 and a portionthereof recycled to supply additional heat to still 30 by means of lines38 and 9. The remainder is withdrawn for use as desired, possibly as anasphalt fraction. A portion of'the overhead 35 from zone 40 may bedirected back to still 30 and is introduced therein below the liquidlevel of the bottoms. The direct contacting of the bottoms in zone 30with stream 35, which is a mixture of combus tion products and vaporizedhydrocarbons, assists in the effective separation of material in thatzone. A portion of stream 35 is taken off by line 36 and passed topreheater 5 in FIGURE 1 where it is condensed and subsequently separatedin separator 18 into the condensed hydrocarbons and flue gas in themanner discussed hereinbefore.

The overhead 39 from pipe still 30 will contain flue gas'from stream 35and vaporized hydrocarbons from the reduced crude. The mixture 39 isdirected to a condenser 60 wherein the hydrocarbon constituents arecondensed and the mixture passed by line 41 to separator 50 where theflue gas is separated from the condensed hydrocarthrough line 43 and areflux stream which is returned to pipe still through line 42. Thecoolant material in condenser 60 is preferably the crude to be treatedin the process and appropriately this would be done after the crude haspassed through preheater 2 (shown in FIGURE 1), but before passing intopreheater 5 (shown in FIG- URE 1).

As in submerged combustion zone 16 discussed hereinbefore water may beinjected via line 45 into reboiler zone below the liquid level. Theadvantages obtained thereby are substantially the same as those obtainedin zone 16.

It is apparent that the sumberged combustion distillation methodsdiscussed hereinahove have wide applicability to the fractionation ofpetroleum oils or other streams which are present in any petroleumrefinery. For example, it may be employed in combination catalyticcracking unit fractionation to permit'handling additional reduced crude,spent caustic and acid sludge incineration,

and tank farm heating or distillation tower reboiling using a hot oilstream.

What is claimed is:

1. In a process to recover an asphalt from a whole crude the stepscomprising preheating said crude to a temperature in the range of about450 to 650 F., passing said crude to a flash separation zone to form agaseous overhead fraction containing those hydrocarbon constituentsboiling below about 450 F. and a liquid reduced crude, withdrawing saidoverhead fraction from said flash separation zone and contacting saidfraction in heat-exchange relationship with said crude to assistpreheating thereof, withdrawing said reduced crude from said flashseparation zone, passing said reduced crude to a heated separation zonewherein a second gaseous fraction containing hydrocarbons boiling belowabout 800 F. and a liquid asphalt fraction are formed, heating saidseparation zone by releasing flue gas from a submerged combustion burnerdirectly into the liquid bottom fraction wherein water is injected intosaid separation zone below the liquid level of the asphalt fraction,withdrawing overhead from said separation zone a gaseous streamcomprising flue gas and said second gaseous fraction and contacting inheat-exchange relationship said gaseous stream with said whole crude topreheat said whole crude and withdrawing from said separation zone saidliquid bottom fraction. I

2. The process of claim 1 wherein said second gaseous fraction iscondensed during said contacting with the whole crude and separated fromsaid flue gas in a second separation zone.

3. The process of claim 1 wherein said flash zone is maintained at apressure of about 5-25 p.s.i.g.

4. A process for segregating a hydrocarbon stream in a distillation zoneinto an overhead gaseous stream and a bottoms liquid stream whichcomprises combusting a fuel in a combustion zone submerged in thehydrocarbon in the presence of oxygen to form a flue gas and releasingsaid flue gas directly into said bottoms liquid to provide the heat forthe distillation, said liquid being at about atmospheric pressure, andinjecting water into said bottoms liquid stream in said distillationzone to control the temperature of distillation and to provide strippingvapors for carrying out the distillation.

5. A process for recovering an asphalt fraction from a whole crude whichcomprises the steps of preheating said crude to a temperature in therange of 450-650 F., passing said crude to a flash zone to form agaseous overhead fraction containing those hydrocarbon constitu entsboiling below about 450 F. and a liquid reduced crude, withdrawing saidoverhead fraction from said separation zone and contacting said fractionin heat exchange relationship with said whole crude to assist preheatingthereof, withdrawing said reduced crude from said flash zone, passingsaid reduced crude to a heated separation zone wherein a second gaseousfraction containing hydrocarbons boiling below about 800 F. and a liquidasphalt fraction are separated, heating said separation zone byreleasing flue gas from a submerged combustion burner directly into theliquid reduced crude and injecting water into said separation zone belowthe liquid level of the reduced crude to control the temperature of thecombustion and to provide stripping gas for said separation zone,withdrawing overhead from said separation zone a gaseous streamcomprising flue gas and said second gaseous fraction andcontacting inheat exchange relationship said gaseous stream with said whole crude topreheat said whole crude and withdrawing from said separation zone saidliquid asphalt fraction.

6. A process for recovering an asphalt fraction from a whole crude whichcomprises preheating said crude to a temperature in the range of 450-650F., passing said crude to a flash zone to separate a gaseous overheadfraction containing those hydrocarbon constituents boiling below about450 F. and liquid reduced crude, withdrawing said overhead fraction fromsaid separation zone and contacting said fraction in heat exchangerelationship with said whole crude to provide preheat for said crude,withdrawing said reduced crude from said flash zone, passing saidreduced crude to an atmospheric pipe still, the bottoms from said pipestill are passed to a reboiler wherein flue gas is introduced into saidbottoms directly from a submerged combustion burner in said reboiler,water is added to said bottoms to control the temperature and to providestripping gas, separating overhead a stream of flue gas, steam andvaporized hydrocarbons, a portion of said overhead stream being recycledto said pipe still and introduced into said bottoms in said pipe stillto provide heat for carrying out distillation in said pipe still and toprovide stripping gas.

7. The process of claim 6 wherein additional heat is added to said pipestill by passing a portion of the hot bottoms from the reboiler to saidpipe still.

8. A process for distilling a high boiling hydrocarbon fraction whichcomprises heating said fraction in a distillation zone, providing heatfor said zone by combusting a fuel in the presence of oxygen in acombustion zone submerged in said hydrocarbon fraction, adding water tosaid liquid hydrocarbon fraction in said distillation zone to controlthe temperature of distillation, prevent cracking' of the hydrocarbons,and to provide additional stripping gas, and separating overhead a lightfraction containing vaporous hydrocarbons, flue gas and stream, and aheavy liquid bottoms product.

References Cited in the file of this patent UNITED STATES PATENTS 71,375,245 Averill Apr. 19, 1921 1,585,224 Alexander May 18, 19261,673,238 Godsey June 12, 1928 1,842,756 Hill Jan. 26, 1932 1,898,168Belden Feb. 21, 1933 2,113,635 Tiddy Apr. 12, 1938 2,738,313 Miller Mar.13, 1956

1. IN A PROCESS TO RECOVER AN ASPHALT FROM A WHOLE CRUDE THE STEPSCOMPRISING PREHEATING SAID CRUDE TO A TEMPERATURE IN THE RANGE OF ABOUT450* TO 650* F., PASSING SAID CRUDE TO A FLASH SEPARATION ZONE TO FORM AGASEOUS OVERHEAD FRACTION CONTAINING THOSE HYDROCARBON CONSTITUENTSBOILING BELOW ABOUT 450*F. AND A LIQUID REDUCED CRUDE, WITHDRAWING SAIDOVERHEAD FRACTION FROM SAID FLASH SEPARATION ZONE AND CONTACTING SAIDFRACTION IN HEAT-EXCHANGE RELATIONSHIP WITH SAID CRUDE TO ASSISTPREHEATING THEREOF, WITHDRAWING SAID REDUCED CRUDE FROM SAID FLASHSEPARATION ZONE, PASSING SAID REDUCED CRUDE TO A HEATED SEPARATION ZONEWHEREIN A SECOND GASEOUS FRACTION CONTAINING HYDROCARBONS BOILING BELOWABOUT 800*F. AND A LIQUID ASPHALT FRACTION ARE FORMED, HEATING SAIDSEPARATION ZONE BY RELEASING FLUE GAS FROM SUBMERGED COMBUSTION BURNERDIRECTLY INTO THE LIQUID BOTTOM FRACTION WHEREIN WATER IS INJECTED INTOSAID SEPARATION ZONE BELOW THE LIQUID LEVEL OF THE ASPHALT FRACTION,WITHDRAWING OVERHEAD FROM SAID SEPARATION ZONE A GASEOUS STREAMCOMPRISING FLUE GAS AND SAID SECOND GASEOUS FRACTION AND CONTACTING INHEAT-EXCHANGE RELATIONSHIP SAID GASEOUS STREAM WITH SAID WHOLE CRUDE TOPREHEAT SAID WHOLE CRUDE AND WITHDRAWING FROM SAID SEPARATION ZONE SAIDLIQUID BOTTOM FRACTION.